Not sure how much knowledge you have with computers, and I couldn't find a picture of the motherboard in the system, but you'll have to take the side off of your computer. Turn your computer off first, and then look for two screws on the back of your case that stick out fairly far (you'll be able to take them out with your fingers), remove those. Look at your mobo and try to locate text saying something along the lines of "PCIe 2.0x16". If you don't see that, look at the bottom of your video card and take note of it's structure, and then look for something that it looks like it'll plug into on your mobo. When you find it, plug it in, and then put the side of your case back on, plug everything back in, and turn it on. Should be self explanatory after that; you might get a box popping up prompting you to install drivers, just follow those instructions and you'll be done.
Hope I hit the mark here with my answer, as I was somewhat confused by your question as well.